1. Field of the Invention
The invention relates to a read only memory (ROM), a method for producing a read only memory, and a method for operating a read only memory in which a selected cell of the read only memory is read out.
Read only memories (ROM), which contain a fixed, predetermined body of information, are very widely used in computers, printers, and all types of electronic devices. Read only memories are predominantly produced by MOS technology. As a rule, the items of information are reproduced by the disposition or omission of a single transistor. The usual memory concepts are based on the LOCOS ROM; the depletion ROM, in which a distinction is made between a NAND ROM and a NOR ROM; the contact hole ROM; and a number of other types, all described in "Semiconductor Memories" by B. Prince, John Wiley & Sons, B. G. Teubner, Stuttgart (2d ed.). A common feature of those memory concepts is that they are constructed in planar fashion on the silicon substrate. Based on the smallest feasible structure width, also known as feature size f, the smallest possible cell accordingly requires a surface area of 4f.sup.2.